This invention relates to a method of connecting a general purpose display (for example, a television set) to a personal computer (PC) in place of a high resolution monitor.
The PC is provided with a graphical user interface (GUI) for displaying its output on a monitor. The Apple Macintosh (Registered Trademark) Operating System and Microsoft Windows (Registered Trademark) are examples of GUI's. In general, PC's that use these types of GUI's output a red-green-blue (RGB) signal to the monitor for displaying images. When a general purpose video display such as the household television set is connected to a PC in place of a monitor, the RGB signal is converted to a National Television Systems Committee (NTSC) signal by a signal conversion circuit. A signal conversion circuit can display a monitor image on a general purpose video display such as a television set or a projection TV.
However, the entire PC screen image cannot be displayed on the general purpose video display by this method. As shown in FIG. 1, when the amount of information displayed by a monitor 13 is compared with that displayed by a general purpose video display 14, the amount displayed by the monitor is clearly greater. For that reason, the entire monitor screen cannot be displayed on a general purpose video display, i.e. a region 15 is not displayed. When the monitor screen 13 is displayed on a general purpose video display 14, the upper and lower edges and the left and right edges extend beyond the bounds of the general purpose video display screen 14 resulting in an over-scan condition.
Incidentally, the resolution of a typical monitor used with a PC is, for example, 640 pixels (horizontally) by 480 pixels (vertically). On the other hand, a typical household television set has a resolution on the order of 570 pixels (horizontally) by 430 pixels (vertically). Therefore, methods which simply convert the RGB signal to NTSC have the drawback that about 10% of the image information cannot be displayed.
To make up for this drawback, methods are used to compress monitor image information for presentation on a general purpose video display. These methods compress all the monitor image information and display it on a general purpose video display. This is accomplished principally by the following two well known methods.
1 A filter is used to delete information at a fixed ratio from the monitor image signal. This method can compress monitor information in a simple manner. However, the monitor image cannot be accurately represented on the general purpose video display. For example, this method has the drawback that fine lines and points disappear entirely.
2 Electron beam scanning of the phosphor screen of the cathode ray tube (CRT) is controlled. Although this method allows enlargement and reduction off the entire image represented on the video display, it can only be realized with a special purpose display. Realization of this method with a general purpose television set is completely out of the question.
The present invention was developed to overcome these and other drawbacks. It is thus an important object of the present invention to provide a method of changing monitor output for use by a general purpose video display such that monitor information can be accurately displayed on a general purpose video display such as a household television instead of on a monitor.